KeyoAPI
Fable 5.1 vs Opus 5.5
Fable 5.1 and Opus 5.5 are two distinct Claude-class catalog IDs on KeyoAPI. The default-group rate for Fable is about 4.17 times the Opus rate. Use the cost table to budget an evaluation, then compare completed work instead of assuming the more expensive option is better for every task.
Opus 5.5 vs Fable 5.1 API pricing
Checked against KeyoAPI's public catalog on 2026-10-13. These are KeyoAPI sell rates for the default billing group, not Anthropic official list prices. The examples cover ordinary input and output tokens; they exclude cached-token differences, extra modalities, billing-group multipliers and retries.
| Model ID | Input / 1M tokens | Output / 1M tokens | 10,000 input + 2,000 output |
|---|---|---|---|
| claude-opus-5-5 | $1.7647 | $8.8235 | $0.035294 |
| claude-fable-5-1 | $7.3530 | $36.7650 | $0.147060 |
For 1,000 requests at that mix, plan $35.294 for Opus or $147.060 for Fable before retries and additional charges. A long agent session may send its growing conversation repeatedly, so estimate the tokens across every turn rather than only the final answer.
Choose a model for coding and agent tasks
Build an evaluation set with your actual acceptance rules: a patch must pass the project tests, a research answer must cite the supplied sources, and a plan must respect its constraints. Give both models the same instructions, context, execution budget and available tools. Record successful tasks, human corrections and the bill for the entire session.
Consider Opus as a lower-cost candidate in this pair and Fable as an option to test on difficult failures. That is a cost-based experiment, not a benchmark claim. Fable is economical only when its measured improvement in accepted results or avoided retries compensates for the higher unit rate. Keep a task and token budget so either model stops after repeated failures.
Call Opus 5.5 using the catalog ID
The shorthand opus5.5 means claude-opus-5-5 in this KeyoAPI guide. Fable 5.1 uses claude-fable-5-1. Both currently advertise the OpenAI-compatible chat route. For an A/B comparison, keep this request unchanged and replace only the model value. Check optional tool and streaming behavior on the route you will deploy.
curl https://www.keyoapi.xyz/v1/chat/completions \
-H "Authorization: Bearer $KEYO_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model":"claude-opus-5-5","messages":[{"role":"user","content":"Review this migration plan: add a nullable field, backfill existing records, validate, then enforce the constraint. Identify missing rollback steps."}],"max_tokens":600}'FAQ
Does Opus 5.5 vs Fable 5.1 need a different comparison?
No. Both word orders refer to the same pair. This page compares claude-opus-5-5 and claude-fable-5-1 with the same token assumptions.
Does Fable 5.1 cost more than Opus 5.5?
At the checked default-group rates, Fable input and output tokens each cost about 4.17 times as much. Use actual session usage to calculate your task cost.
Are these official Anthropic model names and prices?
This comparison documents KeyoAPI catalog IDs and KeyoAPI sell rates. Check first-party provider documentation separately for official naming, availability and prices. More Keyo rates are on the Claude API pricing page.